The devices for tracking eye movement (commonly referred to as “eye trackers”) normally require performing a calibration step. During the calibration process, in fact, some specific eye parameters of the user are deducted to correlate a given pupil position at a certain observed point.
Usually, during the calibration step the user is prompted to at least stare at three predefined points of a screen for a few seconds. The calibration is performed by assuming that the user will actually stare at said points, when required, and that the pupil will not suffer expansion due to a change in lighting conditions.
The calibration procedure described above requires, therefore, attention and cooperation from the user.
Moreover, in most cases the calibration procedure is performed periodically to compensate for any environmental change or to adapt to possible eye fatigue of the user.
The calibration procedure may therefore be annoying and stressful as it requires time and collaboration on behalf of the user.
Moreover, a calibration procedure of this kind is unacceptable for applications open to different users such as interactive interfaces of game or content selection, attention control applications while driving, etc.
The need is felt to minimize the effort required by the user by making the calibration substantially imperceptible.
The document US 2011/0310006, for example, describes a solution wherein the calibration is “masked” through the eye monitoring while the user performs specific actions. It is assumed that the eye is pointing to a set point while these actions take place (e.g. while pressing a button it is assumed that the eye is turned to the button). However, this method still requires collaboration by the user and not always is effective, especially since it often happens that the user performs the action without actually staring at the intended point.